This invention relates to a directional control valve, comprising a valve body having a main bore on which there are provided a plurality of channels connected to respective fluid entry, exit and utilization passages. Within said main bore there is situated an axially movable slider-valving member arranged to assume a number of different axial positions relative to the main bore, of which one is normal and central; when in said axial positions, the slider-valving member determines that number of different conditions of communication between the channels, to control the flow direction. Finally, two thrust means (in particular two linear actuators with electromagnetic ON/OFF action) are applied to the respective ends of the slider-valving member, to act one at a time in order to move the slider-valving member about its central normal position, through a determined distance in a respective direction, to which a respective operative position corresponds.
A typical (though not exclusive) application of these valves is to operate the two operating chambers of double-acting hydraulic actuators.
These valves are able to assume not more than three different conditions of communication between the channels, corresponding to three positions of the slider.
A xe2x80x9cnormalxe2x80x9d condition is obtained when both electromagnetic actuators are inactive; in this condition, the slider is in a central axial position by virtue of the action of spring means, and the centre channels (main passage for the pressurized fluid) are generally open and hence the entering fluid is set to discharge, whereas those channels (xe2x80x9cusersxe2x80x9d) connected to the two chambers of the hydraulic actuator are generally closed.
The other two conditions, which are mutually symmetrical, are obtained when the electromagnetic actuators move the side slider-valving member by acting one at a time; in this condition, the centre channels are closed, whereas one respective user is open to the entering fluid and the other user is connected to discharge.
A valve is known which uses three electromagnetic actuators, in order to obtain a fourth slider position and hence a corresponding fourth communication position, different from the others, to increase the operative facilities of the valve; for example to connect both the users to discharge while the centre channels are open.
However, the use of a third actuator involves higher production costs, greater electrical circuit complications, higher required and installed power, and greater overall size.
An object of this invention is to provide a valve of the aforedescribed type able to define a fourth communication condition while using only two electromagnetic actuators.
This and further objects are attained by the invention as characterised in the claims.
The invention is based on the fact that the slider-valving member comprises two valving elements positioned on one and the other side of the transverse central plane through said slider-valving member, these being subjected to the direct action of the thrust means and movable about this plane between a first operative position defining said normal configuration of the slider-valving member, and a second operative position in which a further different communication condition between the channels is determined, and spring means arranged to normally maintain the two lateral valving elements in said first operative position; moreover, said thrust means are operated either individually or simultaneously, their action being such that when they act individually on the slider-valving member, this maintains its normal configuration, whereas when they act simultaneously on the lateral valving elements, these are moved into said second operative position against the action of the spring means.